SE Icis Condenser - Schematic And Photos

[rodabod]

Thought I may as well post this here. Now before tracing this mic, I listened. It sounds good. It doesn't have that spitty Chinese sound. It had a smooth upper-treble rise, and the low-end extension sounds deep.

Here are the insides. Note the edge-terminated capsule. Can anyone identify this one? I quite like it:

Now to the schematic. Slightly boring plate-out followed by a cathode follower. But, the first triode is slightly more interesting than usual - Ra is 300K.

The transformer is a standard Chinese model. The same you find in most. As per usual, the PSU voltagbes seem a bit high. I've not opened it, but the 6.7V heater hints at the usualy 7806 plus a diode to lift 0.7V.

 

[gyraf]

..R1 is probably 1G, not 1M..

I think I've seen a edge-terminated capsule like that before (mounting screws in groups of three) - but never a single-sided version..?

Jakob E.

 

[burdij]

I believe SE makes all of their capsules in their Shanghai factory:

 

[rodabod]

[quote author="gyraf"]..R1 is probably 1G, not 1M..[/quote]

Yes. Good point.

I think I've seen a edge-terminated capsule like that before (mounting screws in groups of three) - but never a single-sided version..?

Interesting. It just has a clear mylar diaphragm on the other side. I could take a photo if the hole spacing is useful for anyone. I'd like to know if I can purchase this capsule elsewhere. It sounds good to me.

 

[zebra50]

That looks very like the dual sided peluso CK12s I have in my Grizzly G7s, which sound great but seem sensitive to moisture, and are better at 60V than 70-80V, FWIW.

(Roddy - is that the 'whoops' mic with the trashed grill that went for a song?)

Nice to see some of their stuff is OK. I picked up one of their small mics on ebay a while back and was not impressed with the quality control. When it arrived, it was rattling - the capsule had not been properly screwed down and was floating around. Also the circuit board was covered in flux. The capsule looked to be exactly the same as those in MXL2001 mics and others. (I've seen several of these now with bumps and wrinkles in the membrane). Anyway, the body is nice so it'll get a whole new circuit put in sometime.

 

[zebra50]

Just looking at the capsule polarisation, that looks like 193 divided by 2 on the capsule - looks awefully high, unless I'm reading it wrong.

 

[rodabod]

[quote author="zebra50"]That looks very like the dual sided peluso CK12s I have in my Grizzly G7s, which sound great but seem sensitive to moisture, and are better at 60V than 70-80V, FWIW. [/quote]

The CEK12 was my first thought, but the layout of the screws looks different. None of the holes line up in the capsule so no light passes through.

Here is a photo of the back:

(Roddy - is that the 'whoops' mic with the trashed grill that went for a song?)

Yeah, I can't seem to help myself. The dented grill was touching the backplate. Reckon I'm going to sell this one on though once I get a new grill for it. They sell for £300-odd new, so I'm sure it'll sell easily.

Nice to see some of their stuff is OK. I picked up one of their small mics on ebay a while back and was not impressed with the quality control.

The only thing I'm really excited about here is the capsule and with that, the grill design (which is just large and fairly open). The components are mediocre quality, but it still sounds good.

I agree that the polarisation voltage is probably a bit high, but that's typical of Chinese valve condensers. Still seems to sound ok with no diaphragm collapse though.

Roddy

 

[skipwave]

Yeah, that looks like the standard Chinese package up to the capsule. The frame, transformer shield, and pcb all look very much like the ADK GT-2 that I gutted. Circuit is the same, too, except for that 300k Ra. In the ADK and the Nady variants it is 100k.

I have to admit that the stock common-cathode-direct-coupled-to-cathode-follower circuit had a distinctive sound that I'd like to play with in another mic. I first removed the CF and replaced the transformer with a Cinemag 2480, and I have to admit that it kinda sucked at that point due to the capsule (just like the one in Zebra's pic above).

Once that was replaced with a Tenlux capsule it was vastly improved, although the Tenlux is a little light on the bottom end of the spectrum, and bypassing Rk with a 100uF and then a 220uF cap (with a 100nF film in parallel) only exacerbated the problem.

Anyway, that capsule in the Icis looks much nicer than the stock ADK/MXL, but not like the Peluso, which has evenly spaced screws.
http://www.pelusomicrophonelab.com/capsnmnts.html

BTW, I've never used the Peluso, and I'm not making any value judgements here.

Brian

 

[zebra50]

and bypassing Rk with a 100uF and then a 220uF cap (with a 100nF film in parallel) only exacerbated the problem.

Not surprised - I've found myself preferring no bypass cap (and a slightly lower value for the cathode resistor) in several cases when I've done comparisons, although of course it depends what else is going on.

Roddy, does it look like my grill will match your mic? If so, you can have it as a trade against something random in the future.

 

[Gus]

two sides end in three holes?
two sides end in four?
I will check a k67 I thought it was 4 at ends.

 

[zebra50]

Well spotted - weirdly asymmetric.

Is the asymmetry deliberate, or quality control, I wonder.

 

[skipwave]

[quote author="zebra50"]

and bypassing Rk with a 100uF and then a 220uF cap (with a 100nF film in parallel) only exacerbated the problem.

Not surprised - I've found myself preferring no bypass cap (and a slightly lower value for the cathode resistor) in several cases when I've done comparisons, although of course it depends what else is going on.[/quote]

Yeah, it doesn't isolate one variable, making it impossible to draw a simple conclusion. I was, however, surprised that the bass response around 200Hz and down seemed worse with the bypass cap. I now think it has much to do with the Fletcher-Munson curves and hype in our ears' response in the speech intelligibility ranges. The net result is we seem to notice the lift in those upper-mid frequencies much more.

 

[rodabod]

[quote author="skipwave"] I first removed the CF and replaced the transformer with a Cinemag 2480, and I have to admit that it kinda sucked at that point due to the Alctron capsule (just like the one in Zebra's pic above). [/quote]

I've always thought that the standard Shanghai (K87 copy?) capsules sounded shrill and crap. I'd like to implement a filter though - say like the U67 filter curve.

[quote author="zebra50"]

and bypassing Rk with a 100uF and then a 220uF cap (with a 100nF film in parallel) only exacerbated the problem.

Not surprised - I've found myself preferring no bypass cap (and a slightly lower value for the cathode resistor) in several cases when I've done comparisons, although of course it depends what else is going on.[/quote]

Is this really the case? I've never tried not bypassing the cathode resistor, but with a large enough value, I don't see why this would lose low-end. Plus you lose gain. I would like to add a little more low-end to my mic which has a Dale M7 fitted though. I know the M7 naturally rolls off in the low-end, but I find vocalists have to get rather close for sufficient proximity effect.

Roddy, does it look like my grill will match your mic? If so, you can have it as a trade against something random in the future.

That's a very kind offer, but I reckon the odds are that it wouldn't as this mic is pretty huge! Looks like I may buy a spare for £40 (ouch) and get rid of the mic after a bit of fun (I may track some vocals with it in a session if I get the grill soon though). Do let me know if you are looking for any bits and bobs as I have boxes of stuff.

Roddy

 

[skipwave]

[quote author="rodabod"][quote author="zebra50"]

and bypassing Rk with a 100uF and then a 220uF cap (with a 100nF film in parallel) only exacerbated the problem.

Not surprised - I've found myself preferring no bypass cap (and a slightly lower value for the cathode resistor) in several cases when I've done comparisons, although of course it depends what else is going on.[/quote]

Is this really the case? I've never tried not bypassing the cathode resistor, but with a large enough value, I don't see why this would lose low-end. Plus you lose gain. [/quote]

We probably posted at the same time, but I proposed an explanation for this:

I now think it has much to do with the Fletcher-Munson curves and hype in our ears' response in the speech intelligibility ranges. The net result is we seem to notice the lift in those upper-mid frequencies much more.

Basically, I don't think we perceive the loss of gain as consistent across our hearing band, even though it really is. The non-linearity of our hearing could account for some of the perceived imbalance.

A level normalized blind test might shed some light on this. I wish I had time to conduct one.

 

[zebra50]

[quote author="rodabod"]Is this really the case? I've never tried not bypassing the cathode resistor, but with a large enough value, I don't see why this would lose low-end.[/quote]

Sorry - I wasn't really thinking about low end when I read it, more over all 'tone', whatever that is. Really I guess I'm voicing unformed thoughts on G7 / Royer type circuits with pentodes as triodes, using EF86, 5840, 6205, 6AU6A, 6AK5 etc. I've built and rebuilt maybe a dozen of these circuits now over maybe 5 years, and keep coming back to the fact that I prefer the sound of the simple unbypassed circuits to bypassed and some fixed bias (LED) designs.

... I have boxes of stuff.

Likewise! I may start a swaps thread, when I clean up the workshop!

 

[burdij]

This is not a K67 or K87 copy. This is a CK12 copy. The sE capsules plastic rings are white or clear translucent in color. The Alctron version is blue. The original CK12 is a 10x10 grid of holes, however.

 

[Gus]

burdij

I have some Alctron cm-h3b capsules that have the same hole pattern 4 and 3. The 797 from the B2 I have has 6 an 4.

Have you taken a sE capsule apart and found it to have 5 chambers like a real brass CK12?

 

[rodabod]

[quote author="Gus"]Have you taken a sE capsule apart and found it to have 5 chambers like a real brass CK12?[/quote]

I'm not sure which screws on this capsule hold it together, but I was surprised that none of the holes lined up at all on either side. I assumed there was usually an air path through from one side to the other.

 

[Gus]

If it is a ck12 type copy maybe it is a keeper.

Change the output cap to a film I tend to like PET over polypro with some transformers type a FKP MKP 630VDC at the grid to capsule drop the heater to about 5.8 to 6VDC. Maybe the lam alloy is OK when I relammed my 1050 transformers they sounded OK and maybe the winding helped with the high end. Also if you "hit" some transformers with a good level it helps a bit. The 300K plate to a CF to a china transformer might be just fine.

Maybe the stock capsule voltage is what works the best. I tune the voltage on capsules for the circuit gain and level I want to the transformer. The 200meg might be better withe 12a?7 tube than a 1 gig. Do you have a nice 12at7 you can try?

I have fixed grills with shaped pieces of wood pressing the dents out on the inside and reforming the grill on a surface

 

[rodabod]

I thin I might ask if they can supply me with another capsule since I've already explained that my grill was crushed.

I know what components I'd like to swap, but I need to see if I want to keep it first. And it honestly sounds quite good already. Yes, even with shitty Chinese coupling caps.

The mic is running as standard on a Chinese 12AX7. Doesn't seem ideal, but it seems to work ok with the CF buffering the output. The only alternatives I have are the 6072 which came with my TCM1050 and the valves in my EH preamp (12AY7 and 12AU7 I think).

If I have time, I may swap this capsule into another mic and see if the quality of the sound follows.